Re: MX28: leds/pwm: Using pwm driven led as heartbeat leads to kernel warning

[Alexandre Belloni <alexandre.belloni@free-electrons.com>]

On 08/04/2014 at 15:34:04 +0800, Shawn Guo wrote :
> On Fri, Apr 04, 2014 at 06:44:47PM +0200, Alexandre Belloni wrote:
> > On 04/04/2014 at 22:26:58 +0800, Shawn Guo wrote :
> > > On Fri, Apr 04, 2014 at 03:54:52PM +0200, Stefan Wahren wrote:
> > > > the problem is still reproducable in Mainline 3.14.0 and gives the same
> > > > warning message.
> > > > Also i add linux-leds in CC.
> > > > 
> > > > Are there any advices to narrow down the problem?
> > > > 
> > > > Is this problem specific to i.MX28 PWM (i don't have other kind of
> > > > hardware)?
> > > 
> > > I don't think it's specific to i.MX28 PWM.  Since the .config hook of
> > > pwm_ops will be called from interrupt context in this case, any pwm
> > > drivers that do sleeping calls in the hook will have this problem, e.g.
> > > the clk APIs that hold mutex like clk_prepare() and clk_get_rate() etc.
> > > 
> > 
> > Yeah, I'm wondering whether we should set pwm->chip->can_sleep then.
> 
> Right, per kerneldoc of struct pwm_chip, we should set can_sleep.
> 
> /**
>  * struct pwm_chip - abstract a PWM controller
>  * ...
>  * @can_sleep: must be true if the .config(), .enable() or .disable()
>  *             operations may sleep
>  */
> 
> But how does setting the flag make a difference there?  I see pwm core
> does nothing about the flag, or am I missing something?
> 

The driver using the PWM should test the flag, have a look at:
http://lxr.free-electrons.com/source/drivers/leds/leds-pwm.c#L183


-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com